1. Field of the Invention
The present invention relates to a data string retrieval apparatus, used in a microcomputer system such as an IC card, for retrieving a data string from a memory.
2. Description of the Related Art
Of microcomputer systems, an IC card, for example, attracts a great deal of attention. An IC card has a memory which is accessed by a control section, such as a CPU. The memory stores a plurality of data strings. An arbitrary data string of the stored data strings is selectively accessed.
In such an IC card, when a data string in the memory is to be retrieved, the speed of retrieval processing may be increased by assigning retrieval processing to a specific circuit or the like. In this case, the memory must be designed to be accessed by a control section and a retriever means.
In a microcomputer system such as an IC card, however, an access data supply bus is commonly used by the control section and the retrieval means. For this reason, when the retrieval means is operated, the control section must release the bus. Consequently, the control section cannot perform calculation processing or access a memory other than the memory from which data is retrieved during an operation of the retriever means.
Furthermore, in a retrieval apparatus designed such that, for example, a single key word is recognized and a data string including this key word is then retrieved, if two or more key words are required to be conditioned for retrieval processing, serious inconvenience inevitably occurs. That is, the control section must check a data string obtained upon retrieval using an arbitrary key word whether it satisfies the second and subsequent key words. This applies to a case wherein a data string is retrieved by a combination of a plurality of key words.
According to such a retrieval scheme, a desired data string may not be retrieved unless processing of the retrieval apparatus and determination of the control section are performed a plurality of times. Consequently, the processing speed of the IC card is decreased.
As described above, according to the conventional retrieval schemes, retrieval using a plurality of key words cannot be easily performed, and moreover, a combination condition of key words cannot be set. Therefore, such schemes are not suitable for retrieval of a data string having a plurality of attribute data, such as a data string in a memory of an IC card. Hence, high-speed retrieval processing cannot be realized.
In addition, according to a retrieval scheme employed by a conventional data string retrieval apparatus, the length of a data string to be retrieved is recognized in advance by the apparatus, and the data string is sequentially retrieved based on the recognized data string length.
In some current data file systems, however, data strings are stored using a variable-length format by adding data string length data to the start portion of each data string. The conventional data string retrieval apparatus cannot process such a variable-length data string.
In a data file management system for, e.g., an IC card, in order to allow the IC card to cope with various applications, a memory is divided into a plurality of areas to be managed. Fixed-length or variable-length data is employed depending on an area.
In order to cope with such a case, a conventional system employs a scheme wherein two apparatuses, i.e., fixed-length and variable-length data string retrieval apparatuses are arranged, and a control section selectively uses the two apparatuses. In this scheme, however, the control section must selectively use the two data string retrieval apparatuses, and the size of the overall data string retrieval apparatuses is increased, thus undesirably increasing the size of the total system.